Conventionally, laparo-endoscopic surgery called water-filled laparo-endoscopic surgery (WaFLES) has been known. In this method, endoscopic surgery is performed while fluid such as isotonic fluid is perfused in the body cavity (for example, refer to Patent Literatures 1 and 2). Filling the body cavity with the fluid can prevent drying of organs and thus adhesion thereof. The water-filled surgery has such an advantage that organs can be moved without being damaged. In addition, this fluid effectively serves as propagation medium of ultrasonic waves, which is relatively easily damped in air.
Bleeding during an operation in the body cavity and a resected tissue fragment floating in the body cavity cloud the fluid and blur an endoscope view. According to Patent Literatures 3 to 6, the fluid in the body cavity is circulated through a filtering apparatus. Specifically, as illustrated in FIG. 4, a suction tube 110 is placed in a body cavity 100 to suck the fluid in the body cavity. The sucked fluid is filtered through a filtering apparatus 112 to remove red blood cells and tissue fragments in the fluid. The fluid after the filtering is returned into the body cavity.